Blue smoke on startup

rangebyte · Post by **rangebyte** » Sat May 16, 2009 11:03 pm

Hi!

What does a small puff of blue smoke on a petrol engine at start-up mean.....near death :S

Kitch · Post by **Kitch** » Sat May 16, 2009 11:46 pm

Valve stem seals probably. They harden over the years and start to perish, meaning oil that was once being pumped around the engine while it was running seeps through them and down the sides of the valve once the engine is switched off, where as normally it would just drain back to the sump. Quite a common thing really, not a major ball ache to change on a petrol model although it's a head off job to do it properly IMO and give it a good de-coke. You'll probably find it puffs a little after lifting off the throttle having given it some beans, as the vacuum created by the engine running down draws minute quantities in and then burns them in the hot chamber.

If it smokes all the time, it's more possible its the piston rings, which to be honest isn't that hard to put right either, although it's engine out, head and sump off to do it thoroughly. Costs a bit more, but it'll restore lost compression and should behave almost like new. I've done them on mine and the difference is noticable, even though it wasn't smoking!

rangebyte · Post by **rangebyte** » Sat May 16, 2009 11:47 pm

so is it maybe best to avoid a vehicle with this problem?

DavidRutherford · Post by **DavidRutherford** » Sun May 17, 2009 8:36 am

I've never worried about crispy valve stem oil seals, as it does at least mean you know that the valve guides are being oiled, and hence the stems and guides are unlikely to wear. I've built a couple of TD enignes now specifically without stem seals for that very reason.

Worn piston rings is another matter entirely though...